High idle
Senior User
Joined: Oct 2012
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Yes my vacuum hose was full of fuel so that's how I knew right away. but you are right, it seems a lot of people have been replacing their old ecu's as of late. Not the cheapest fix but if you find a used one they ain't much
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Senior User
Joined: Oct 2010
Posts: 439
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I never thought it would be the FPR because the engine runs really strong and has no staring issues. The plugs are also the right color.
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Senior User
Joined: Oct 2010
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I know this is not my thread but if the truck idles back down when the IAC is unplugged that means the ECU is telling it to open up and speed up idle, correct? I testing the FPR on my truck last summer and it held vacuum so I don't think it was the issue in my case, also if the diaphragm is damaged it will leak fuel into through the vacuum hose causing a very rich condition all the time.
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Senior User
Joined: Oct 2010
Posts: 439
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So to resurrect this thread.....
Heres an update. I still have the high idle problem 1200 rpm at stop in gear. RPM surges to 1200 when I release the clutch in neutral or slowing down in neutral. I have replaced the map sensor, vacuum canister, tps sensor, cleaned the IAC valve, replaced the throttle body, and checked for vacuum leaks off of the tree and throttle body to no real results. Any other ideas? I am getting 11 mpg with a 5.0 and 302 4.10 gears m5od. I do 55 mph at 2100 rpm. I do mostly highway driving. The truck didn't pull any codes related to idle last time I scanned it.....
Freshman User
Joined: Jan 2009
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Does it idle high with the IAC unplugged? I only ask that to eliminate half of the possible causes. If it still idles high then it has to be a vacuum leak, what about the PCV lines or upper to lower intake gasket? If it does not idle high witht he IAC unplugged then it is a sensor related item and it has to be throwing some sort of code.
I probably sound like a broken record but that is all I can think of to check.
I probably sound like a broken record but that is all I can think of to check.
Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
Does it idle high with the IAC unplugged? I only ask that to eliminate half of the possible causes. If it still idles high then it has to be a vacuum leak, what about the PCV lines or upper to lower intake gasket? If it does not idle high witht he IAC unplugged then it is a sensor related item and it has to be throwing some sort of code.
I probably sound like a broken record but that is all I can think of to check.
I probably sound like a broken record but that is all I can think of to check.
The simple test is unplugging the IAC. If the idle drops down or the engine stalls out then the issue is computer/sensor/electrical related. If the idle remains high the issue is unmetered air aka vacuum leak.
If the root cause is the latter it's a process of elimination. I seem to recall the OP has tried multiple throttle bodies and a few IACs with the same result. I suspect an air intake gasket problem or an as yet unfound vacuum line/reservoir leak is causing the issue.
Take my input for what you paid for.............free.
YMMV
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Senior User
Joined: Oct 2010
Posts: 439
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I had it out yesterday afternoon. It idled lower than normal, round 1000 rpm. It then started to idle perfect at 800 rpm. However, it bogged down some. My throttle body is clean and the fuel filter only has 3000 miles on it. I have not done anything except the leaking vacuum reservoir. Ideas? This is puzzling me
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Senior User
Joined: Oct 2010
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I did this and the idling dropped down. I have installed a new TPS sensor, used IAC valve, map sensor. The only thing I can think of left would be the computer..... any ideas?
Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
It does make a difference...
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Junior User
Joined: Mar 2013
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From: mt airy, georgia
My truck is 92 5.0 automatic and it idles high too. Only in park, will idle at 1000-1300rpm, when its in gear it idles 800rpm when stopped. Has new TPS and IAC and i just went out and adjusting the throttle stop screw because it was touching when engine warm. It dropped the idle accordingly to 800rpm. But when i turned truck off and started back it idled about 1000rpm. So that means my TB springs are bad correct? Just double checking before I purchase new TB
Elder User
Joined: Aug 2012
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What is all this about replacing the whole throttle body when the spring gets weak, is the spring not replaceable?
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Senior User
Joined: Oct 2010
Posts: 439
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I have to run a self test soon. Just super busy with classes and work! I will post results by the weekend. Anyhow, my old mechanic said my throttle body was worn out. This seems odd as I saw a truck with 300k in the scrapyard. The throttle body was no worse than mine. The throttle bodies don't wear out but the spring cannot be replaced from what I have seen
Mountain Pass
Joined: Apr 2013
Posts: 193
Likes: 0
From: Midlothian, TX
did you have this problem before the intake manifold gasket was replaced? that would be my guess. the IM gasket or the upper plenum gasket. if thet are breached, it will be a vacuum leak and cause high idle. a way you can test for this(not always accurate) is to get some wd40 for carbcleaner and spray around the base of the the manifolds and see if this affects the idle. the fluid will temporarily 'plug' the whole in the gasket if there is one. you can also get a cheap hand pump vacuum gauge from autozone or oreillys and hook it up to where the pcv valve line goes into to upper intake. see if it will hold vacuum. that can eliminate the thought of a vacuum leak if it holds a small about of vacuum for 5 minutes or so. dont pump it up to high.